No Spark from Coil

7173Mustangs.com

Help Support 7173Mustangs.com:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

hetrickw

Well-known member
Joined
Jun 13, 2012
Messages
84
Reaction score
2
Location
San Antonio
My Car
71
I have a 351small block that cranks but doesn't fire. Battery is good. I checked voltage into + coil and it's above 12v with key forward....I checked spark at plug wire ends...no spark at all.... I pulled coil wire at distributor and get no spark when grounded to block.........I did ohm test to coil and it appears ok......voltage off + coil is above 12v..... think it's coil but omh test says otherwise.......overheated engine.. now no spark.

 
Cap and rotor condition?

Ignition type?
Old but clean. points couple months old, didn't replace condenser (7 years old). Is there a way to check voltage from coil to distributor?


original points condenser....no upgrades

coil.jpg

 
Last edited by a moderator:
make sure trans in Park or Neutral, possible neutral safety switch issue.

i would swap coil and retest for spark. i had a bunch of coils fail in different ways, maybe the secondary step up coil went but the primary is fine.

from there condenser. maybe ohm test the coil to cap ignition wire or swap and see if the wire is the problem.

 
Cap and rotor condition?

Ignition type?
Old but clean. points couple months old, didn't replace condenser (7 years old). Is there a way to check voltage from coil to distributor?


original points condenser....no upgrades
will change out coil @ see what she does......thanks for assistance.

 
If you have a timing light, it can be used as a spark tester too. Putting the pick up on the coil to distributor wire should have it flashing pretty fast even during cranking.

If you haven't checked the rotor recently, take a look as sometimes strange things happen. Ive seen the "button" on a rotor fall off and have seen caps where contacts did not truly make contact.

 
With the distributor cap off and the points in the closed position, ignition key on "run" not start,,, Open and close the points with a small plastic or wood blade.. If you see a spark jump between the point surfaces, the problem rests with the coil.. Hope that helps.

 
Make sure the points are opening and closing, should have 0.016 inch gap when on the high point of the cam.
thanks, all...i'll just replace Cap/coil/points/condenser and see if that gets it. can't be much more since I've got voltage to the coil right?

checked resistance on coil/dist. wire and it looks good.

I always appreciate the great suggestions/knowledge on this site...

Bill

 
Check the amperage as well. I had that issue with an old flat head. 6.4 volts (good for that system) at only 0.1 amp will not make a spark. I had enough contact at the wire from the switch to get voltage but not enough for the proper amperage. It took forever to track it all the way back to the loose connection under the dash.

 
bad coil....replaced points/plugs/condenser...works great with .017 gap....thanks all...........

Bill

71.JPG

 
glad it was an easy fix.

one thing i would keep an eye on, the gap/dwell.

the made in china points everyone is afflicted with tend wear REALLY quick and drift wildly.

so as the points wears down suddenly the gap closes up and POOF coil blows.

another thing to watch for, is setting the gap with a feeler might not be a good idea, better to set it using the dwell angle you may find with the new points that the gap can be right but the dwell will be too short or too open. this is because the materials they use to today are sub par and the contact points are not conducting well, or the metal is soft and contacts dance around.

so for example say you set the gap at .17 then measure dwell and see 44; When the range should be 24-29 that is bad because the gap is too short, To decrease the dwell you increase the gap and vise-versa.

this is the argument for electronic ignitions.

personal experience: I ran points for a long time, and the quality of the points was a major problem, i was diagnosing another engine issue and wanted to keep points.

so i put in a new set, used dwell set for 24 degrees and the next week i went on a trip 135 miles.

i came back car was running fine decided to check dwell, it was over 56 (Way too short) yet the car didn't seem to notice.

readjusted dwell to 24,, drove another week, again the dwell moved to 50 range,,, readjusted,, next week coil blew.

i tried one more time i Bid on Ebay for a set of Accel vintage points replacement with a double spring and all the bells and whistles of a 1970s vintage part.

well by the time it came i was fighting with the garbage points on a weekly basis,

i told myself this is chasing your tail and installed a pertronix II, Done.

i kept the accel points NIB and it is in my trunk with a condenser in-case the electronic ever goes out, its been over 7 years i have never needed it.

now if your ignition system is in great shape, which is most likely is, then you will see no immediate gains from going electronic, for the most part it will run the same.

the difference between the two occurs over time, with the gap constantly changing and you having to maintain it, eventual start up issues with points and more maintenance.

on the performance end, points will bounce at high rpms and can occasionally miss. so the gains are not seen right away just over the long haul.

 
Back
Top